The present invention relates to a process for producing L-threonine by fermentation. L-threonine is not only useful as a medicament such as amino acid preparations but also utilizable as an additive for animal feed.
With respect to the fermentation process for production of L-threonine by use of a microorganism belonging to the genus Escherichia, various processes have been known; for example, a process using a microorganism having a borrelidin sensitivity (Japanese Published Examined Patent Application No. 6752/76), a process using a microorganism requiring diaminopimelic acid and methionine for growth and of which threonine biosynthesis system is resistant to feedback inhibition of threonine (Japanese Published Examined Patent Application No. 10037/81), a process using a microorganism having a resistance to at least one of rifampicin, lysine, methionine, aspartic acid and homoserine, or a decreased ability to degrade L-threonine (Japanese Published Unexamined Patent Application No. 273487/88, U.S. Pat. No. 5,017,483), a process using a microorganism having a resistance to at least one of L-serine and ethionine (Japanese Published Unexamined Patent Application No. 259088/91, European Publication No. 445830), etc.
However, the known processes are still insufficient in efficiency of the production of L-threonine. It is therefore an object of the present invention to provide a process for producing L-threonine, in higher yield and at lower cost.